This invention relates to a carburetor fuel pump for small combustion engines and more particularly to a carburetor fuel priming pump having a duckbill dual check valve.
Carburetors for small combustion engines are known to have manual priming pumps which expel unwanted air from fuel passages and chambers within the carburetor so that the engine may be easily started. The fuel priming pumps utilize a manually depressable domed cap which defines a pump chamber and a dual check valve which controls fuel and air flow from the carburetor and into a fuel tank of a non-running engine. When the dome is depressed against its own resilient force, an orifice of the valve is compelled to open to discharge air, vapor and/or liquid fuel from the pump chamber and preferably into the fuel tank. As the domed cap returns to its initial or unflexed natural state, the pump chamber is under vacuum causing the orifice within the outlet passage to close and a resilient annular member of the valve to flex outward to open an inlet passage.
When the engine is running, the inlet passage to the pump chamber preferably remains closed via the annular member, preventing unwanted recirculation of fuel from the carburetor to the fuel tank through the priming pump. It has been discovered that unfortunately, any vacuum or decrease in pressure created within the fuel tank during running conditions may cause the orifice of the dual check valve to oscillate open and closed. This oscillation can cause a decrease in the priming pump chamber pressure to a point where unwanted fuel leaks past the annular member from the inlet passage into the pump chamber and through the oscillating orifice. Such fuel leakage deprives the carburetor of needed fuel, causing erratic and unsteady running conditions of the engine.
A carburetor for a small internal combustion engine has a fuel priming pump with a resilient dual check valve allowing fuel flow in a first direction and preventing fuel flow in a second direction. The resilient dual check valve is reinforced with longitudinally extending ribs to prevent recirculation of fuel through an orifice of the valve in a running engine. The orifice is defined by a distal end of a tubular portion of the valve press fitted and projecting into an outlet passage that communicates with a pump chamber defined by a resilient domed cap. The ribs project laterally outward from the tubular portion within the outlet passage. Preferably an annular isolation member is engaged to an opposite end of the resilient valve. The isolation member flexes outward to open an inlet passage to communicate with the pump chamber.
By depressing a resilient domed cap, the volume is decreased and pressure is increased within the pump chamber causing the rib reinforced orifice to open expelling air and fuel from the chamber into the outlet passage. Upon release of the dome, it begins to return to its unflexed state which causes the chamber volume to increase thereby producing a vacuum draw or lower pressure relative to the pressure of the inlet passage. Consequently, the isolation member flexes outward during dome restoration and the orifice closes as a result of the rib bias and change in pressure differential. With the isolation member flexed outward, air, vapor and/or liquid fuel flows from the open inlet passage into the pump chamber. When the dome is fully extended, or in its unflexed natural state, the inlet passage and the outlet passage are closed and isolated from the pump chamber via the resilient dual check valve.
During engine running conditions, any vacuum or sub-atmospheric pressure created within the fuel tank and communicated through the outlet passage will cause a small negative pressure differential between the outlet passage and the higher pressure in the pump chamber. The orifice, however, will remain closed due to the bias of the reinforcement ribs preventing unwanted recirculation of air, vapor and fuel through pump chamber.
Objects, features and advantages of this invention include providing a priming pump with a resilient dual check valve capable of preventing unwanted air, fuel vapor and fuel flow through the priming fuel pump of a carburetor during engine running conditions, enhancing stability of a running engine, reducing exhaust emissions, and providing a dual check valve of relatively simple design, extremely low cost when mass produced, and which is rugged, durable, reliable, requires no maintenance or adjustment, and in service has a long useful life.